Numerous devices have been disclosed in the prior art for maintaining broken bone segments of the upper arm in a fixed, healing position. The most common type of device is the well known plaster cast. In addition, various braces have also been proposed, including various semi-rigid braces.
When using a plaster cast on the upper arm, it is the usual procedure to put the cast along the length of the arm with the arm bent at the elbow. When this occurs, the arm hangs from the shoulder so that the weight of the cast and arm must be supported. This support is provided by a collar and cuff. As the collar and cuff support the weight of the cast, the point of attachment of the cuff to the cast determines how the bone segments angulate relative to one another. With no support, there is a strong tendency for the bone segments to angulate. Therefore, by changing the point of attachment of the cuff along the length of the lower arm, the tendency of the bones to angulate coin be overcome.
Rather than trying to have the bone segments not angulate at all, the angulation into valgus is generally desired because the broken bone segments are usually still connected along the exterior side by soft tissues. On the interior side, there is usually a breakage of the corresponding soft tissue connection so that there is a latent tendency of the bone to again move into a varus orientation. Therefore, by urging the bone segments into a valgus orientation, the tendency of the bone segments into a varus orientation is compensated for. In addition, the valgus orientation actually helps urge the proximal ends of the bone segments into contact with one another against the pull of the soft tissue connecting the exterior sides of the bone segments.
In using a plaster cast, the cast is left in place and supported by the collar and cuff for several weeks. During this time, the arm and shoulder are immobilized. This usually results in several weeks of rehabilitation. Obviously, this long time period for rehabilitation is undesired.
When applying a plaster cast to broken bone segments in the limb, it is known to shape the plaster cast so that a slight pressure is present on the same side of the bone break where the soft tissue has broken away from the bone. In this manner, the fracture site is urged toward the soft tissue which is unbroken on the other side of the break. Such a cast is shaped so that there are essentially three points of force applied against the bone, forces on either end of the bone pushing against the side of the bone where the soft tissue is still connected, and the force located at the break in the bone pushing in the opposite direction toward the connected soft tissue. This is referred to as "three point fixation".